1. Field of the Invention
The present invention relates to a transfer device in an automatic tool exchanger for simultaneously exchanging a tool received in a machine tool spindle with another tool disposed at an exchange station.
2. Description of the Prior Art
Transfer devices of the character described for use in automatic tool exchangers have heretofore been provided wherein a pair of mutually parallel transfer arms are mounted to be rotatable about and slidable along a common axis. These transfer arms are further arranged to grip tools received in a tool spindle and a storage magazine when rotated in opposite directions at an axially withdrawn position, to extract the tools therefrom when axially extended to an extended position, and to replace mutual positions of the tools when rotated in the same direction at the extended position.
In one such known transfer device, disclosed in U.S. Pat. No. 3,786,938 to Edward E. Kirkham, a rack and pinion mechanism is provided to rotate a pair of transfer arms in opposite directions for the purpose of simultaneous tool gripping, and pinions are rotated in meshing engagement with the same rack for 180.degree. rotation while mutual positions of the tools are replaced. Because of backlash existing between the rack and the pinions, the tools are never gripped without a gap being present between themselves and the transfer arms, so that reliable or tight tool gripping cannot be achieved. Further, in the tool removal operation, the pinions are transferred from engagement with another set of racks to engagement with the aforementioned rack, which thus requires that all the racks are exactly aligned prior to the tool removal operation, and therefore, considerable restraint is effected in adjusting the rotational angles of the transfer arms for tool gripping and tool transferring.
In another form of transfer device, first and second rack and pinion mechanisms are respectively associated with tandem cylinder assemblies for individually rotating a pair of transfer arms, allowing the transfer arms to be rotated independently, so that each one of a pair of tools can be reliably or tightly gripped without having a gap being present between itself and the transfer arms. However, three cylinders must be provided in each of the tandem cylinder assemblies for effecting tool gripping, tool removal and tool releasing, and therefore, the transfer device, although freed from gear transferring of pinions, is complicated in construction and difficult to control.